Studies will be made of factors which influence and determine the transport of solutes and water across isolated renal tubules including 1) the effect of aryl acids on fluid secretion in pars recta of the proximal tubule, 2) the mechanism of cell volume regulation in hypotonic media, and 3) the nephronal location and mechanism of uric acid transport. BIBLIOGRAPHIC REFERENCES: Grantham, J.J. Renal transport and excretion of potassium. In: The Kidney. Brenner and Rector (eds). W. B. Saunders, 1976. Grantham, J. J. Fluid secretion in the nephron: Relation to renal failure; Physiol. Reviews 56:248-258, 1976.